Many potentially interesting monoclonal antibodies can rapidly be produced by the mouse immune system for biological study. In a clinical setting however, the use of these murine antibodies can result in a human anti-mouse antibody response (HAMA) thus negating their utility. A method to transfer the murine antigen binding information to a non-immunogenic human antibody acceptor, a process known as humanization, has resulted in many therapeutically useful drugs. The method of humanization generally begins by transferring all six murine complementarity determining regions (CDRs) onto a human antibody framework (Jones et al., Nature 321, 522-525 (1986)). These CDR-grafted antibodies generally do not retain their original affinity for antigen binding, and in fact, affinity is often severely impaired. Besides the CDRs, select non-human antibody framework residues must also be incorporated to maintain proper CDR conformation (Chothia et al., Nature 342:877 (1989)). The transfer of key mouse framework residues to the human acceptor in order to support the structural conformation of the grafted CDRs has been shown to restore antigen binding and affinity (Riechmann et al., Nature 332:323-327 (Mar. 24, 1988); Foote and Winter, J. Mol. Biol. 224:487-499 (1992); Presta et al., J. Immunol. 151, 2623-2632 (1993); Werther et al., J. Immunol. 157:4986-4995 (1996); and Presta et al., Thromb. Haemost. 85:379-389 (2001)). Many of the framework positions that are likely to affect affinity have been identified, thus structural modeling to select new residues in a stepwise fashion can generally lead to variants with restored antigen binding. Alternatively, phage antibody libraries targeted at these residues can also be used to enhance and speed up the affinity maturation process (Wu et al., J. Mol. Biol. 294:151-162 (1999) and Wu, H., Methods in Mol. Biol. 207:197-212 (2003)).
Two approaches have been taken when choosing a starting human acceptor. One approach compares the sequence of the murine antibody to a list of known human antibody sequences in order to choose the human antibody most homologous to the murine antibody (Shearman et al., J. Immunol. 147:4366 (1991); Kettleborough et al., Protein Eng. 4, 773 (1991); Tempest et al., Biotechnology 9:266 (1991); Co et al, Proc. Natl. Acad. Sci. USA 88:2869 (1991); Routledge et al., Eur. J. Immunol. 21:2717 (1991)). This approach is designed to reduce the likelihood of disrupting the integrity of the CDRs upon grafting them onto the new human acceptor. A second approach utilizes a consensus human framework derived from human VL and VH subgroups. By choosing the most frequently used sequence as a acceptor, this approach has been shown to reduce the potential of an immunological response to the humanized antibody (Presta et al., J. Immunol. 151:2623-2632 (1993)). Following transfer of CDR residues into an acceptor chosen by either of these methods, it has been necessary to alter framework residues in the acceptor in order to restore and enhance antigen binding affinity.
Humanized anti-IgE, anti-CD 11 a and anti-tissue factor (TF) antibodies have been described in Presta et al., J. Immunol. 151, 2623-2632 (1993), Werther et al., J. Immunol. 157:4986-4995 (1996), and Presta et al., Thromb. Haemost. 85:379389 (2001), respectively.
Patent publications describing humanized antibody variants include U.S. Pat. No. 6,407,213 and WO92/22653 (Carter and Presta), WO98/45332 (Wells et al.), WO98/45331 (Baca et al.), as well as US2003/0228663A1 and WO03/087131A2 (Lowman et al.).
US 2004/0162413, Watkins et al., published August, 2004 refers to methods of optimizing antibody variable region binding affinity. WO03/105782 A2, Rybak et al., published December 2003, references specificity grafting of a murine antibody onto a human framework.